JP2014119494A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide image formation for color shift correction enhanced in resistance against noise, while suppressing a detection error caused by an AC component.SOLUTION: An image forming apparatus includes a photoreceptor, process means acting on the photoreceptor, formation means for forming an electrostatic latent image on the photoreceptor, detection means for detecting the electrostatic latent image formed on the photoreceptor by a current flowing in the process means, color shift correction means for forming a detection pattern including a plurality of latent image marks being electrostatic latent images for color shift correction on the photoreceptor and performing the color shift correction based on time information when the detection means detects each of the latent image marks of the detection pattern, and storage means for storing the weighting coefficient of each of the latent image marks of the detection pattern. The color shift correction means weights the time information when each of the latent image marks of the detection pattern is detected by a corresponding weighting coefficient, to perform the color shift correction.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system.

  As an electrophotographic image forming apparatus, a so-called tandem system in which an image forming unit for each color is provided independently is known. In this tandem image forming apparatus, an image is sequentially transferred from an image forming portion of each color to an intermediate transfer belt, and further, an image is transferred collectively from the intermediate transfer belt to a recording medium.

  In such an image forming apparatus, color misregistration (positional misregistration) occurs when the images are overlapped due to mechanical factors in the image forming unit of each color. In particular, in a configuration in which a photoconductor and a scanner unit that exposes the photoconductor are provided in each image forming unit, steady color misregistration (hereinafter referred to as DC color misregistration) occurs due to variations among the image forming units. . In order to correct DC color misregistration, the image forming apparatus performs color misregistration correction control. Specifically, a developer image for detection (hereinafter referred to as a detection pattern) for detecting the position of each color is formed on an image carrier such as an intermediate transfer belt, and the relative position of the detection pattern for each color is optically determined. By detecting with a sensor, the amount of color shift is detected and corrected.

  On the other hand, periodic speed fluctuations occur in the photoconductor and the like due to the eccentricity of the roller that drives the photoconductor and the intermediate transfer belt. Due to this speed fluctuation, an unsteady color shift (hereinafter referred to as AC color shift) occurs. The AC color misregistration causes an error in the color misregistration amount detected by the detection pattern in the color misregistration correction control. For this reason, Patent Document 1 proposes that detection patterns are arranged in a number corresponding to an integer at an interval of 1 / integer of a cycle of speed fluctuation that is a cause of AC color misregistration. In Patent Document 1, color shift correction control is performed by averaging the detection results from the detection patterns thus formed.

  Further, electrical noise is generated during the color misregistration correction control, and an error may be given to the detection result of the detection pattern. Further, if an impact or the like due to the operation of the mechanical mechanism of the image forming apparatus is generated during the formation of the detection pattern, the detection pattern forming position is shifted. Even in this case, an error is given to the detection result of the detection pattern. Hereinafter, a detection error caused by an electrical noise or an impact of a mechanical mechanism in the color misregistration correction control is simply referred to as noise. Increasing the number of detection patterns is effective in increasing the noise tolerance of color misregistration correction control.

JP 2001-356542 A

  However, there is a case where a restriction condition is imposed on the arrangement of patches, which are developer images constituting the detection pattern, and the number of patches cannot be increased freely. Hereinafter, this constraint condition will be described with reference to FIG.

  For example, if the peripheral length of the intermediate transfer belt is 600 (mm) and the colors used for image formation are four colors, the condition that the maximum length of one color detection pattern is 150 (mm) is imposed. Each color detection pattern includes a plurality of patches. However, if the interval between patches is too short, detection accuracy deteriorates. Therefore, for example, a condition that the minimum interval between patches is 15 (mm) is added here. As shown in FIG. 16, the length of one cycle of speed fluctuation that causes AC color misregistration is 100 (mm), and the maximum value of the detection error caused by this speed fluctuation is ΔA. Further, as shown in FIG. 16, it is assumed that noise giving a detection error ΔB occurs. Detection pattern # 1 in FIG. 16 is a pattern in which patches are arranged at equal intervals over one cycle of speed fluctuation while satisfying the condition of the minimum interval 15 (mm) in order to reduce detection error due to AC color misregistration. is there. That is, six patches y1 to y6 are arranged at an interval of 100/6 = 16.67 (mm).

  The amount of color misregistration is obtained by averaging the detection position or time of each patch. However, in detection pattern # 1, since the patch is formed over one cycle of the speed fluctuation, the detection error due to the speed fluctuation is canceled and zero. Become. On the other hand, the detection error due to noise affects only one patch at most, and thus becomes smaller as the number of patches in the detection pattern increases. Specifically, ΔB / 6 is obtained in the detection pattern # 1. Here, in order to increase resistance to noise, it is considered that the number of patches is further increased at the same patch interval as the detection pattern # 1, as in the detection pattern # 2. Detection pattern # 2 is obtained by increasing three patches y7 to y9 at the same interval as the patch of detection pattern # 1.

  In detection pattern # 2, the detection error due to noise is ΔB / 9, which is smaller than detection pattern # 1. However, the length of the detection pattern # 2 is not an integral multiple of the speed fluctuation period. Here, when the detection error of the color misregistration amount due to the speed fluctuation when the detection pattern # 2 is used is obtained by numerical calculation (ΔA × 2/9), the detection pattern # 1 is deteriorated. As described above, when the number of patches is increased to improve noise resistance, detection errors due to AC components may increase. In order to suppress the detection error due to noise without increasing the detection error due to the AC component, for example, a detection pattern is formed with a length of 200 (mm) in two cycles of speed fluctuation, that is, in the example of FIG. Can also be considered. However, since the maximum length of one color detection pattern is 150 (mm) in this example, such a configuration is not possible.

  The present invention provides an image forming apparatus that performs color misregistration correction with improved resistance to noise while suppressing detection errors due to AC components.

  According to one aspect of the present invention, an image forming apparatus includes a photosensitive member, a process unit that acts on the photosensitive member, a forming unit that forms an electrostatic latent image on the photosensitive member, and a current flowing through the process unit. Detection means for detecting an electrostatic latent image formed on the photosensitive member and a detection pattern including a plurality of latent image marks which are electrostatic latent images for color misregistration correction are formed on the photosensitive member, and the detection means detects the detection A color misregistration correction unit that corrects color misregistration based on time information at which each latent image mark of the pattern is detected, and a storage unit that stores a weighting factor of each latent image mark of the detection pattern, The misregistration correction unit is characterized by correcting color misregistration by weighting the time information at which each latent image mark of the detection pattern is detected with a corresponding weighting coefficient.

  The tolerance to noise can be enhanced while suppressing detection errors due to AC components.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 3 is a diagram illustrating a high-voltage power supply system to an image forming unit according to an embodiment. The functional block diagram of the engine control part by one Embodiment. The flowchart of the reference value acquisition process by one Embodiment. FIG. 6 is a diagram illustrating a detection pattern for color misregistration correction and a latent image mark according to an embodiment. Explanatory drawing of the detection of a latent image mark. 5 is a flowchart of color misregistration correction control according to an embodiment. The timing chart of formation and detection of a latent image mark by one embodiment. FIG. 3 is a diagram illustrating a driving configuration of a photoconductor according to an embodiment. Explanatory drawing of the speed fluctuation which arises in the drive of the photoconductor by one Embodiment. The figure which shows the latent image pattern by one Embodiment. Explanatory drawing of the detection error by noise. The figure which shows the latent image pattern by one Embodiment. The figure which shows the weighting coefficient by one Embodiment. The figure which shows the detection error by one Embodiment. Explanatory drawing of arrangement | positioning restrictions of a detection pattern.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit invention. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
FIG. 1 is a configuration diagram of an image forming unit of the image forming apparatus according to the present embodiment. Note that the English letters a, b, c, and d at the end of the reference numerals form the developer images of the members in yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. It shows that it is a thing. In addition, when it is not necessary to distinguish colors, reference numerals excluding the last alphabetic characters a, b, c, and d are used. The photoconductor 22 is an image carrier and is driven to rotate. The charging roller 23 charges the surface of the corresponding color photoconductor 22 to a uniform potential. As an example, the charging bias output from the charging roller 23 is −1200 V, and thereby the surface of the photosensitive member 22 is charged to a potential of −700 V (dark potential). The scanner unit 20 forms an electrostatic latent image on the photosensitive member 22 by scanning and exposing the surface of the photosensitive member 22 with a laser beam corresponding to the image data of the image to be formed. As an example, the potential of the portion where the electrostatic latent image is formed becomes −100 V (bright potential) by exposure with laser light. Each of the developing devices 25 has a corresponding color developer, and the developing sleeve 24 supplies the developer to the electrostatic latent image on the photosensitive member 22 to develop the electrostatic latent image on the photosensitive member 22. . As an example, the developing bias output from the developing sleeve 24 is −350 V, and the developing unit 25 attaches the developer to the electrostatic latent image by this potential. The primary transfer roller 26 is an image carrier that transfers the developer image formed on the photosensitive member 22 to an intermediate transfer belt 30 that is driven by rollers 31, 32, and 33. As an example, the primary transfer bias output from the primary transfer roller 26 is +1000 V, and the primary transfer roller 26 transfers the developer to the intermediate transfer belt 30 by this potential. At this time, a color image is formed by transferring the developer images of the respective photosensitive members 22 onto the intermediate transfer belt 30 in a superimposed manner.

  The secondary transfer roller 27 transfers the developer image on the intermediate transfer belt 30 to the recording medium 12 conveyed through the conveyance path 18. The fixing roller pairs 16 and 17 heat and fix the developer image transferred to the recording medium 12. Here, the developer that has not been transferred from the intermediate transfer belt 30 to the recording medium 12 by the secondary transfer roller 27 is collected in the container 36 by the cleaning blade 35. In addition, a detection sensor 40 is provided to face the intermediate transfer belt 30 in order to perform color misregistration correction control by forming a conventional developer image.

  The scanner unit 20 may be configured to expose the photosensitive member 22 by an LED array or the like instead of a laser. Further, instead of providing the intermediate transfer belt 30, an image forming apparatus that directly transfers the developer image of each photoconductor 22 to the recording medium 12 may be used.

  FIG. 2A illustrates a high-voltage power supply system to each process unit of the image forming unit. Here, the process unit is a member that acts on the photosensitive member 22 for image formation, including any of the charging roller 23, the developing device 25, and the primary transfer roller 26. The charging high voltage power supply circuit 43 applies a voltage to the corresponding charging roller 23. The development high voltage power supply circuit 44 applies a voltage to the developing sleeve 24 of the corresponding developing device 25. Further, the primary transfer high-voltage power supply circuit 46 applies a voltage to the corresponding primary transfer roller 26. Thus, the charging high-voltage power supply circuit 43, the development high-voltage power supply circuit 44, and the primary transfer high-voltage power supply circuit 46 function as a voltage application unit for the process unit.

  Next, the charging high-voltage power supply circuit 43 in this embodiment will be described with reference to FIG. The transformer 62 boosts the voltage of the AC signal generated by the drive circuit 61 to an amplitude several tens of times. The rectifier circuit 51 including the diodes 1601 and 1602 and the capacitors 63 and 66 rectifies and smoothes the boosted AC signal. The rectified and smoothed signal is output as a DC voltage from the output terminal 53 to the charging roller 23. The operational amplifier 60 controls the output voltage of the drive circuit 61 so that the voltage obtained by dividing the voltage at the output terminal 53 by the detection resistors 67 and 68 is equal to the voltage setting value 55 set by the engine control unit 54. . Then, according to the voltage of the output terminal 53, a current flows through the charging roller 23, the photoconductor 22 and the ground.

  The current detection circuit 50 is provided to output a detection voltage 56 corresponding to this current. The detection voltage 56 is input to the negative input terminal of the comparator 74. A reference voltage 75 is input to the positive input terminal of the comparator 74. The comparator 74 outputs a binarized voltage 561 corresponding to the detected voltage 56 and the reference voltage 75 to the engine control unit 54. Specifically, the comparator 74 becomes “high” when the detection voltage 56 is lower than the reference voltage 75, and becomes “low” otherwise.

  As will be described later, in this embodiment, color misregistration is corrected by a latent image mark that is an electrostatic latent image for color misregistration correction formed on the photosensitive member 22. As will be described later, while the latent image mark passes through the position of the charging roller 23, the current flowing through the charging roller 23, the photoconductor 22 and the ground increases, and the detection voltage 56 is higher than that at other times. Decrease. The reference voltage 75 which is a threshold value is between the detection voltage 56 when there is no latent image mark and the minimum value when the latent image mark passes the position of the charging roller 23 so that the passage of the latent image mark can be detected. Is set to the value of With this configuration, when the latent image mark passes the position of the charging roller 23, the comparator 74 outputs a binary voltage 561 having one rising edge and one falling edge thereafter to the engine control unit 54. For example, the engine control unit 54 sets the midpoint between the rise and fall of the binarized voltage 561 as the latent image mark detection position. Note that the engine control unit 54 can detect only one of the rising edge and the falling edge of the binarized voltage 561 and set it as the detection position of the latent image mark.

  Next, the current detection circuit 50 in FIG. 2B will be described. The current detection circuit 50 is inserted between the secondary circuit 500 of the transformer 62 and the ground point 57. By outputting a desired voltage to the output terminal 53, a current flows through the current detection circuit 50 via the photosensitive member 22, the charging roller 23, and the ground point 57. The inverting input terminal of the operational amplifier 70 is connected to the output terminal via the resistor 71. Therefore, a detection voltage 56 that is an output value proportional to the amount of current flowing through the output terminal 53 appears at the output terminal of the operational amplifier 70. The capacitor 72 is for stabilizing the inverting input terminal of the operational amplifier 70.

  The engine control unit 54 comprehensively controls the operation of the image forming apparatus. The CPU 321 uses the RAM 323 as a main memory and work area, and controls image formation according to various control programs stored in the EEPROM 324. In addition, the ASIC 322 performs control of each motor, high voltage power supply control of the developing bias, and the like in image formation under the instruction of the CPU 321. Note that part or all of the functions of the CPU 321 may be performed by the ASIC 322, and conversely, part or all of the functions of the ASIC 322 may be performed by the CPU 321 instead. A part of the function of the engine control unit 54 may be assigned to hardware corresponding to another control unit.

  It should be noted that in realizing the functions described here, the form of hardware is not limited, and any of CPU 321, ASIC 322, and other hardware may be operated. The processing may be shared among the hardware by arbitrary distribution.

  Next, the operation of the engine control unit 54 will be described with reference to FIG. 3 collectively represents actuators such as a drive motor for the photosensitive member 22 and a separation motor for the developing unit 25. 3 collectively represents sensors such as a registration sensor, a current detection circuit 50, and the like. The engine control unit 54 performs various processes based on information acquired from each sensor 330. The actuator 331 functions as, for example, a drive source that drives a cam for separating the developing sleeve 24 described later.

  The forming unit 327 controls the scanner unit 20 to form a latent image mark described later on each photoconductor 22. Further, a process for forming a developer image for color misregistration correction on the intermediate transfer belt 30 described later is also performed. As will be described later, the process control unit 328 controls the operation / setting of each process unit when a latent image mark is detected. The color misregistration correction control unit 329 calculates the color misregistration correction amount and reflects the color misregistration correction amount from the detection time of the binarized voltage 561 by a calculation method described later.

  The outline of the color misregistration correction control in the present embodiment will be described below. First, the engine control unit 54 forms a color misregistration detection pattern based on the developer image on the intermediate transfer belt 30 and measures the relative position of other colors with respect to the reference color by the detection sensor 40 to determine the color misregistration amount. . Then, the engine control unit 54 adjusts image forming conditions, for example, the timing at which the scanner unit 20 irradiates the photosensitive member 22 with laser light so as to reduce the determined color misregistration amount.

  In a state where the color shift after the color shift correction using the developer image is small, the photoconductor 22 acquires a reference value for the color shift correction by the latent image mark. Specifically, a plurality of latent image marks are formed on each photoconductor 22, and the reference voltage is obtained by determining the time when the formed latent image marks reach the position of the charging roller 23 using the detection voltage 56. Thereafter, in the color misregistration correction control performed when the temperature in the apparatus changes due to continuous printing or the like, the color misregistration is determined by determining the color misregistration amount based on the latent image mark to be formed and the reference value. In the following, correction of color misregistration is performed by controlling the irradiation timing of the laser beam. For example, even if the speed of the photosensitive member 22 is controlled, the reflection mirror included in the scanner unit 20 is controlled. The mechanical position may be controlled.

  Details of the color misregistration correction control will be described below with reference to FIG. Note that the processing of FIG. 4 is performed independently for each color except S1. In S <b> 1 of FIG. 4, the engine control unit 54 forms a detection pattern that is a developer image for color misregistration detection on the intermediate transfer belt 30. FIG. 5A is an example of a detection pattern. In FIG. 5A, marks 400 and 401 are patterns for detecting the amount of color misregistration in the moving direction (sub-scanning direction) of the intermediate transfer belt 30. Marks 402 and 403 are patterns for detecting a color misregistration amount in the main scanning direction orthogonal to the moving direction of the intermediate transfer belt 30. 5A is the moving direction of the intermediate transfer belt 30 and corresponds to the sub-scanning direction. In the example of FIG. 5A, the marks 402 and 403 are inclined by 45 degrees with respect to the main scanning direction. Note that the last characters of the reference numerals of marks 400 to 403, Y, M, C, and Bk indicate that the corresponding marks are formed of yellow, magenta, cyan, and black developers, respectively. Further, tsf1 to 4, tmf1 to 4, tsr1 to 4, and tmr1 to 4 of each mark indicate detection timings of the corresponding marks detected by the detection sensor 40. The detection of the marks by the detection sensor 40 can be performed using a known technique such as, for example, using reflected light when the mark is irradiated with light.

Hereinafter, the correction of the position of magenta will be described by using yellow as a reference color. However, the same applies to correction of other cyan and black positions. The moving speed of the intermediate transfer belt 30 is v (mm / s), and the theoretical distance between the yellow marks 400 and 401 and the magenta marks 400 and 401 is dsM. In this case, the color misregistration amount δesM in the sub-scanning direction of magenta is
δesM = v × {(tsf2−tsf1) + (tsr2−tsr1)} / 2−dsM
It is represented by

Further, regarding the main scanning direction, for example, the magenta color shift amount δemfM on the left side is
δemfM = v × (tmf2−tsf2) −v × (tmf1−tsf1)
It is represented by The same applies to the magenta color misregistration amount δemrM on the right side. The sign of δemfM and δemrM represents the direction of deviation in the main scanning direction. The engine control unit 54 corrects the writing position of the magenta color from δemfM, and corrects the width in the main scanning direction, that is, the main scanning magnification, from δemrM−δemfM. When there is an error in the main scanning magnification, the writing position is calculated not only by δemfM but also by taking into account the amount of change in the image frequency (image clock) that has changed as the main scanning magnification is corrected. For example, the engine control unit 54 changes the emission timing of the laser beam by the scanner unit 20 so as to eliminate the calculated color misregistration amount. For example, if the amount of color misregistration in the sub-scanning direction is four lines, the engine control unit 54 adjusts the emission timing of the laser beam that forms the magenta electrostatic latent image by four lines. In this manner, the subsequent reference value acquisition process can be performed with the color misregistration amount reduced by the process of step S1.

  Returning to FIG. 4, in S <b> 2, the engine control unit 54 sets the rotation phase between the photoconductors 22 to a predetermined state in order to suppress the influence when the rotation speed (surface speed) of the photoconductor 22 varies. Match. Specifically, under the control of the engine control unit 54, the phase of each photoconductor 22 is adjusted so that the formation timing of the latent image mark on each photoconductor 22 is the same. When the drive gear of the photoconductor 22 is provided on the rotation shaft of the photoconductor 22, the phase relationship of the drive gear of each photoconductor 22 is adjusted so as to be a predetermined relationship.

  After adjusting the phase of each photoconductor 22 in S2, the engine control unit 54 forms a latent image pattern, which is a detection pattern for color misregistration correction, including a plurality of latent image marks on each photoconductor 22 in S3. How the latent image marks included in one latent image pattern are determined will be described later. In the following description, it is assumed that one latent image pattern includes 24 latent image marks. When forming the latent image pattern, the developing sleeve 24 is separated from the photoconductor 22 so that the latent image mark is not developed, and the primary transfer roller 26 is also separated from the photoconductor 22. For the primary transfer roller 26, the applied voltage may be set to off (zero) so that the action on the photosensitive member 22 is smaller than that during normal image formation. Further, the developer sleeve 24 may be prevented from adhering to the developing sleeve 24 by applying a bias voltage having a reverse polarity. Further, when using the jumping development method in which the photosensitive member 22 and the developing sleeve 24 are brought into a non-contact state and the voltage application is performed by superimposing the AC bias on the DC bias, the voltage application to the developing sleeve 24 is turned off. You just need to.

In step S <b> 4, the engine control unit 54 calculates the exposure timing tL (i) that is the time when each latent image mark is formed and stores it in the RAM 323. Here, the exposure timing is the formation timing of the center position of the latent image mark in the sub-scanning direction. Specifically, when the exposure start timing of the i-th latent image mark is tLup (i) and the exposure end timing is tLdown (i), the exposure timing tL (i) is
tL (i) = (tLup (i) + tLdown (i)) / 2
It becomes. Note that tLup (i) and tLdown (i) may be the rising and falling timings of the laser signal forming the latent image mark.

  FIG. 5B shows a state in which the latent image mark 80 is formed on the photosensitive member 22. For example, the latent image mark 80 is formed to have the maximum width in the image region width in the main scanning direction, and to have a width of about 30 scanning lines in the sub-scanning direction. In the main scanning direction, in order to increase the fluctuation range of the detection voltage 56 due to the latent image mark 80, it is desirable that the main scanning direction be formed with a width of half or more of the maximum width of the image area. In addition, the width of the latent image mark 80 can be expanded to an area further beyond the image area (print area on the recording medium).

  Next, the engine control unit 54 detects each edge of each latent image mark 80 formed on each photoconductor 22 based on the detection voltage 56 in S5. FIG. 6A shows the time variation of the detection voltage 56 when the latent image mark 80 reaches the charging roller 23. As shown in FIG. 6A, when the latent image mark 80 passes through a position facing the charging roller 23, the detection voltage 56 is lowered accordingly and then changes so as to return. Here, the reason why the detection voltage 56 varies as shown in FIG. 6B and 6C show the surface potential of the photosensitive member 22 when the developer is not attached to the latent image mark 80 and when it is attached. In these drawings, the horizontal axis indicates the surface position in the circumferential direction of the photosensitive member 22, and the region 93 indicates the position where the latent image mark 80 is formed. The vertical axis indicates the potential. The dark potential of the photosensitive member 22 is VD (for example, −700 V), the bright potential is VL (for example, −100 V), and the charging bias potential of the charging roller 23 is VC (for example, −1000 V).

  In the area 93 of the latent image mark 80, the potential differences 96 and 97 between the charging roller 23 and the photosensitive member 22 are larger than the potential difference 95 in the other areas. For this reason, when the latent image mark 80 reaches the charging roller 23, the value of the current flowing through the charging roller 23 increases. As the current increases, the voltage value at the output terminal of the operational amplifier 70 decreases. The above is the reason why the detection voltage 56 decreases. As described above, the detection voltage 56 reflects the surface potential of the photosensitive member 22. Note that the current path between the charging roller 23 and the photosensitive member 22 is based on both the route through the nip between the charging roller 23 and the photosensitive member 22, the discharge in the vicinity of the nip, and both. Things can be considered, but it doesn't matter what form. Further, as apparent from FIG. 6C, the position of the latent image mark 80 can be detected by the detection voltage 56 even if the developer adheres to the latent image mark 80. That is, the latent image mark 80 may be in a developed state at the position of the charging roller 23, and detecting the latent image mark 80 includes detecting the developed latent image mark 80. It is a waste.

The detection voltage 56 is once decreased by the latent image mark 80 and returns to the original value, so that the comparator 74 in FIG. 3 outputs two edges, rising and falling, when one latent image mark 80 passes. . Therefore, when 24 latent image marks 80 are formed for each color, the engine control unit 54 detects 48 edges for each color. Here, assuming that the detection time of each edge is te (i), the engine control unit 54 sets the detection timing tC (i) of the i-th (i = 1 to 24) latent image mark 80 in S6 of FIG. ,
tC (i) = (te (2i-1) + te (2i)) / 2
Calculate as That is, the detection timing of the latent image mark 80 is the detection timing of the center position of the latent image mark 80.

In subsequent S7, the engine control unit 54 sets a time interval ty (i) which is time information from when the i-th latent image mark 80 is formed to when it is detected.
ty (i) = tC (i) −tL (i)
Calculate and save with

In S8, the engine control unit 54 obtains a standardized weighting coefficient w (i) (i = 1 to 24) stored in the EEPROM 324 in advance. Details of the weighting factor will be described later. In S9, the engine control unit 54 multiplies the time interval ty (i) from formation to detection of each latent image mark by the weighting factor w (i) and integrates them, thereby including all the latent image patterns. The weighted average value ty of the time interval from the formation of the latent image mark 80 to the detection is calculated as follows.
ty = Σw (i) × ty (i)
The engine control unit 54 stores the obtained weighted average value ty as a reference value, for example, in the EEPROM 324.

  Next, color misregistration correction control will be described with reference to FIG. Note that the processing of FIG. 7 is also performed independently for each color. The processing of S11 to S18 in FIG. 7 is the same as the processing of S2 to S9 in FIG. However, the value obtained in S18 is dty. In S19, the engine control unit 54 compares the dty obtained in S18 with the reference value ty obtained in advance in the process of FIG. Specifically, it is determined whether or not the difference obtained by subtracting the reference value ty obtained in advance in the process of FIG. 4 from the dty obtained in S18 is 0 or more. If the difference is 0 or more, this means that the average value of the time from exposure to detection of the latent image mark 80 is delayed from the reference value, so the engine control unit 54 sets the exposure timing in S20. Make it fast. On the other hand, if the difference is less than 0 in S19, the exposure timing is delayed in S21. Through the above processing, color misregistration can be corrected. Note that the color misregistration correction control using the latent image mark 80 is not limited to the above embodiment. For example, it is possible to form a latent image mark 80 of each color at the same time and observe the difference in detection timing.

  Next, formation of the latent image pattern will be described with reference to the timing chart of FIG. FIG. 8 shows a sequence for a certain color, but the sequence of FIG. 8 is performed for each color. The engine control unit 54 outputs a drive signal for driving the cam for separating the developing sleeve 24 at time T1, and the developing sleeve 24 is separated from the photosensitive member 22 at time T2. Further, the engine control unit 54 controls the primary transfer bias from the on state to the off state at time T3. Instead of separating the developing sleeve 24 at time T1, the output voltage of the developing high-voltage power supply circuit 44 may be set to 0, or a voltage having a polarity opposite to that of the normal voltage may be applied. Further, the primary transfer roller 26 may be separated from the primary transfer bias instead of turning off.

  Furthermore, the engine control unit 54 starts forming a total of 24 latent image marks 80 from time T4. Further, a total of 24 latent image marks 80 formed are detected between times T5 and T6. The current detection signal corresponds to the detection voltage 56 or the binarized voltage 561. Thereafter, the engine control unit 54 calculates ty (i). For example, ty (1) is a difference 700 between the time when the first latent image mark 80 indicated by L01 is formed and the time when the first latent image mark 80 indicated by C01 is detected.

  FIG. 9 shows the configuration of a drive unit that drives the photosensitive member 22. The drive motor 800 transmits power to the photoconductor gear 804 via the motor gear 801 and the step gear 802. The photoconductor 22 is arranged coaxially with the photoconductor gear 804 and is configured to rotate together with the photoconductor gear 804. The photoconductor gear 804 is provided with a home position flag 806 so that one rotation period of the photoconductor 22 can be monitored by the home position sensor 805. For example, the rotation of the drive motor 800 is reduced to 1/16 by the gears 801 to 804 to drive the photosensitive member 22.

  Hereinafter, the configuration of the latent image pattern in this embodiment will be described. First, detection errors due to AC components to be considered in the present embodiment will be described. The AC component means a periodic component that repeatedly occurs such as a sine wave. Each gear shown in FIG. 9 has an eccentricity, and the gear engagement radius fluctuates due to the eccentricity of each gear, so that a speed fluctuation occurs in the rotation of the photosensitive member 22.

  FIG. 10 shows the speed fluctuation of the surface of the photoreceptor 22 due to the eccentricity of the gear. The three waveforms from the top in the figure show the speed fluctuations of the photoconductor gear 804, the step gear 802, and the motor gear 801, respectively. In the gear configuration of FIG. 9, the step gear 802 is rotated four times and the motor gear 801 is rotated 16 times while the photosensitive member gear 804 is rotated once. The speed fluctuation amplitude of each gear is an amount corresponding to the gear eccentricity and the reduction ratio (rotation ratio) between the gears. Usually, the amplitude of the gear component having a large gear diameter and a large reduction ratio is large. Therefore, the speed fluctuation due to the photoconductor gear 804 having the largest amplitude can be a component that should be most considered in the detection error of the gear drive transmission system.

  The detection error due to the gear drive transmission error is affected twice when the latent image pattern is formed and when it is detected. That is, depending on the relationship between the exposure position for forming the latent image mark 80 and the mounting position of the charging roller 23 for detecting the latent image mark 80, the speed fluctuation of each gear overlaps in the same phase, and the detection error deteriorates. On the other hand, they may overlap and reverse each other in the opposite phase and improve.

  Next, the AC component generated by the charging roller 23 will be described. When the rotation axis of the charging roller 23 is decentered or the roller has a shape error, the contact point between the charging roller 23 and the photosensitive member 22 moves in the period of the charging roller by the amount of the decentering or error. As a result, a detection error occurs. For example, if the shaft eccentricity of the charging roller 23 is 50 (μm), the contact point moves with an amplitude of 50 (μm), which causes a latent image pattern detection error. The last waveform in FIG. 10 shows how the speed of the charging roller 23 fluctuates.

[Basic pattern design]
In this embodiment, the latent image pattern determined in consideration of only the AC component is referred to as a basic pattern, and a pattern obtained by extending the basic pattern in order to increase noise resistance is referred to as an extended pattern. In the following description, the width of each latent image mark 80 in the sub-scanning direction is 30 lines. The 30 lines are substantially equal to the width of the area where the photosensitive member 22 and the charging roller 23 are in contact. The minimum value of the width of the area between the adjacent latent image marks 80 is also 30 lines. This is because if the adjacent latent image marks 80 are too close, the detection current interferes and each latent image mark 80 cannot be detected correctly. Further, the length of the latent image pattern in the sub-scanning direction, that is, the rotation direction of the photoconductor 22 is set to be equal to or less than the circumferential length of the photoconductor 22.

  First, when the gear configuration is as shown in FIG. 9 and the four AC components shown in FIG. 10 are generated, a basic pattern for reducing detection errors due to these AC components will be described with reference to FIG. First, in order to reduce the AC component of the photoconductor gear 804, the latent image mark 80 is added at a position separated from the reference latent image mark 80 shown in FIG. The added state is shown in FIG. Next, in order to reduce the AC component of the step gear 802, the latent image mark 80 is added to a position separated from each latent image mark 80 in FIG. The added state is shown in FIG. Next, in order to reduce the AC component of the motor gear 801, the latent image mark 80 is added to a position separated from each latent image mark 80 in FIG. The added state is shown in FIG. Finally, in order to remove the AC component of the charging roller 23, the latent image mark 80 is added at a position separated from each latent image mark 80 in FIG. The added state is shown in FIG. In this way, it is possible to design a basic pattern including the latent image marks 80 arranged so that the detection errors of the latent image marks caused by the four AC components cancel each other. Then, four AC components can be obtained by detecting all the 16 latent image marks and adding all the detected values or by dividing by the total number of latent image marks forming them. The detection error can be canceled and reduced. In this way, the basic pattern has an interval of 1 / integer of the length corresponding to one period of speed fluctuation by each gear and the charging roller 23, and is equal to the integer, that is, one period of speed fluctuation. The latent image mark 80 is arranged over the entire area. In the above example, the integer is 2, but other values may be used. In the case of having a plurality of speed fluctuations, the basic pattern includes a first number of latent image marks 80 arranged at intervals obtained by dividing the period of each speed fluctuation by an integer (first number). .

  Next, detection errors due to noise components will be described. As described above, sudden displacement may occur due to the influence of electrical noise and the operation of a mechanical mechanism in the image forming apparatus on the exposure. In the present embodiment, the detection error caused by the sudden and randomly generated positional deviation is simply referred to as noise.

  A state in which a detection error occurs due to noise will be described with reference to FIG. FIG. 12A shows the time change of the detection voltage 56, and the waveform indicated by reference numeral 551 is electrical noise that occurs suddenly during the detection process. When the generation timing of the noise 551 occurs when the latent image mark is detected, the waveform of FIG. 12A is superimposed on the waveform of FIG. 6A, resulting in a waveform 552 of FIG. The waveform 550 is a waveform when noise is not superimposed. When the noise is superimposed, the timing at which the detection voltage 56 intersects the reference voltage 75 indicated by Vref in FIG. 12B changes, which becomes a detection error. The amount of this detection error varies depending on the amplitude of the noise waveform, the width in the time direction, and the noise generation timing. Since the frequency of noise generation is small, in this embodiment, the latent image mark 80 on which noise is superimposed by one detection operation is at most one.

[Extended pattern design]
Noise causes a large detection error. Therefore, in order to reduce detection errors due to noise, it is effective to increase the number of basic pattern latent image marks 80. FIG. 13A shows the basic pattern of FIG. FIG. 13B is obtained by offsetting the basic pattern of FIG. 13A in the sub-scanning direction. Note that the amount of offset is an amount by which a part of the latent image marks 80 in FIG. 13B overlaps a part of the latent image marks 80 in FIG. That is, the latent image marks b1, b3, b5, b7, b9, b11, b13, and b15 in FIG. 13B are the latent image marks a2, a4, a6, a8, a10, a12 in FIG. , A14 and a16 overlap each other. FIG. 13C is an extended pattern obtained by synthesizing the latent image patterns of FIGS. 13A and 13B. Each of the basic patterns of FIGS. 13A and 13B includes 16 latent image marks 80, but the 8 latent image marks 80 overlap at the same position. The extended pattern (C) includes 24 latent image marks 80.

  As already described with reference to FIG. 16, if the 24 latent image marks 80 are simply averaged, the AC component cannot be removed. Therefore, in this embodiment, weighted averaging is performed.

  Hereinafter, weighted averaging according to the present embodiment will be described. The extended pattern shown in FIG. 13C is a combination of the basic pattern shown in FIG. 13A and the basic pattern shown in FIG. Here, each of the basic patterns shown in FIGS. 13A and 13B can substantially remove the AC component by performing the averaging process independently. Therefore, the AC component can be substantially removed by adding the two latent image marks 80 twice and averaging them. The weight coefficient corresponds to the number of times of overlapping and adding.

  Therefore, for example, for the extended pattern shown in FIG. 13 (C), as shown in FIG. The weight coefficient is set to 1 for other latent image marks. In the case of such calculation, the total number of latent image marks is not 24 actually formed, but 32 which is a simple sum of two superimposed basic patterns. Therefore, it is necessary to divide by 32 to obtain the average value. Therefore, as shown in FIG. 14, the normalized weighting coefficient is a value obtained by dividing the weighting coefficient by 32. Using this normalized weighting factor, average times ty and dty from exposure to detection are obtained. By using the weighted coefficient obtained as described above, it is possible to suppress the detection error of the AC component and suppress the noise component as much as possible.

  For example, assuming that noise that causes detection error Δ is on one latent image mark 80, the detection error is Δ / 16 in the basic pattern including 16 latent image marks 80 shown in FIG. . On the other hand, in the extended pattern shown in FIG. 13C in which eight more latent image marks 80 are added, when the noise that causes the detection error Δ rides on one latent image mark 80, the detection error is shown in FIG. It becomes street. First, when noise is added to the overlapping latent image marks m2, m5, m8, m11, m14, m17, m20, and m23, since these are added twice in the averaging process, the detection error is Δ / 16. It becomes. Therefore, the detection error in this case is the same as the basic pattern shown in FIG. However, when noise is placed on the non-overlapping latent image mark 80, the detection error is Δ / 32, which is half of the basic pattern. Since the noise generation position is random, the probability 16/24 = 66.67% that noise is applied to a non-overlapping latent image mark is 8/24 = the probability that noise is applied to the overlapping latent image mark 80. Higher than 33.33%. Therefore, resistance to noise can be increased by the extended pattern. The extended pattern according to the present embodiment can be formed with a length less than twice the basic pattern.

  In order to further improve noise resistance, the number of latent image marks to be superimposed may be reduced. In other words, the ratio of the superimposed latent image marks in the latent image pattern may be lowered. As a result, the probability of noise occurrence in overlapping latent image marks is reduced, the probability of obtaining a noise reduction effect is increased, and noise resistance is further improved. It is also effective to increase the number of latent image marks. Although two latent image patterns are used in FIG. 13, three or more latent image patterns may be superimposed.

  Further, in FIG. 13, the basic pattern is offset so that some of the latent image marks 80 overlap, but if the offset can be made so that the latent image marks 80 do not overlap, the independent latent image mark is simple. The error due to noise can be further reduced. That is, the extended pattern may be overlapped so that the latent image marks 80 of the basic pattern do not overlap. However, in a configuration that is difficult to arrange so as not to overlap as in the example of FIG. 13, noise tolerance can be increased by allowing some latent image marks 80 to overlap.

  By configuring the latent image pattern as described above, it is possible to improve noise resistance while reducing the AC component.

  In the above-described embodiment, the latent image pattern is formed when there are four AC components, but the number is not limited. Further, the cause of the AC component is not limited to the driving configuration of the photosensitive member 22 and the knitting center of the charging roller 23. In order to reduce the AC component as much as possible, the position of the latent image mark 80 of the basic pattern is determined based on the period of the AC component, but other arrangements that can reduce the AC component are also possible. Furthermore, in the above-described embodiment, the same basic pattern is overlapped to form the extended pattern. However, two or more different basic patterns may be overlapped. This is effective when there is no room in the arrangement space and the basic pattern cannot be offset and overlapped. Furthermore, this embodiment can be applied not to a latent image pattern but also to a detection pattern constituted by a developer image.

  Further, in the above-described embodiment, the current flowing through the charging roller 23 is detected by the current detection circuit 50 provided in the charging high-voltage power supply circuit 43. However, the current detection circuit 50 may be provided in the development high-voltage power supply circuit 44 or the primary transfer high-voltage power supply circuit 46 to detect the current flowing through the development sleeve 24 and the primary transfer roller 26.

<Other embodiments>
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

Claims (15)

A photoreceptor,
Process means acting on the photoreceptor;
Forming means for forming an electrostatic latent image on the photoreceptor;
Detecting means for detecting an electrostatic latent image formed on the photosensitive member by current flowing through the process means;
A detection pattern including a plurality of latent image marks, which are electrostatic latent images for color misregistration correction, is formed on the photosensitive member, and color misregistration correction is performed based on time information when the detection unit detects each latent image mark of the detection pattern. Color misregistration correction means for performing
Storage means for storing a weighting coefficient of each latent image mark of the detection pattern;
With
2. The image forming apparatus according to claim 1, wherein the color misregistration correction unit corrects the color misregistration by weighting time information when each latent image mark of the detection pattern is detected with a corresponding weighting coefficient. The detection pattern is a combination of a plurality of basic patterns including a plurality of latent image marks,
The basic pattern is arranged at an interval of the first number arranged at an interval obtained by dividing at least one period of one or more periodic speed fluctuations caused by rotation of the photoconductor or the process means by the first number. The image forming apparatus according to claim 1, further comprising a latent image mark. The detection pattern is a combination of a plurality of basic patterns including a plurality of latent image marks,
A plurality of latent image marks included in the basic pattern are detected in time information detected from each latent image mark due to at least one of one or more periodic speed fluctuations caused by rotation of the photoconductor and the process means. The image forming apparatus according to claim 1, wherein the errors are arranged so as to cancel each other.   The image forming apparatus according to claim 2, wherein the detection pattern is synthesized so that the latent image marks of the plurality of basic patterns do not overlap each other.   4. The image forming apparatus according to claim 2, wherein the detection patterns are synthesized such that some latent image marks of each of the plurality of basic patterns overlap each other.   6. The image forming apparatus according to claim 5, wherein the weighting factor of each latent image mark is determined by the number of superimposed latent image marks when the basic pattern is synthesized.   The image forming apparatus according to claim 1, wherein a length of the detection pattern in a rotation direction of the photoconductor is equal to or less than a circumferential length of the photoconductor.   The time information is a time from when the forming unit forms a latent image mark to when the detecting unit detects the latent image mark. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the color misregistration correction unit calculates a color misregistration amount by comparing the weighted time information with a reference value.   The process means is a charging means for charging the photosensitive member, a developing means for supplying a developer to the electrostatic latent image on the photosensitive member, or a transfer means for transferring the developer image formed on the photosensitive member to another member. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A photoreceptor,
Process means acting on the photoreceptor;
Forming means for forming an electrostatic latent image on the photoreceptor;
Detecting means for detecting an electrostatic latent image formed on the photosensitive member by current flowing through the process means;
A detection pattern including a plurality of latent image marks, which are electrostatic latent images for color misregistration correction, is formed on the photosensitive member, and color misregistration correction is performed based on time information when the detection unit detects each latent image mark of the detection pattern. Color misregistration correction means for performing
With
The detection pattern is a combination of a plurality of basic patterns including a plurality of latent image marks,
The basic pattern is arranged at an interval of the first number arranged at an interval obtained by dividing at least one period of one or more periodic speed fluctuations caused by rotation of the photoconductor or the process means by the first number. An image forming apparatus comprising a latent image mark.   A plurality of latent image marks included in the basic pattern are detected in time information detected from each latent image mark due to at least one of one or more periodic speed fluctuations caused by rotation of the photoconductor and the process means. The image forming apparatus according to claim 11, wherein the errors are arranged so as to cancel each other.   The image forming apparatus according to claim 11, wherein the detection pattern is synthesized such that each latent image mark of each of the plurality of basic patterns does not overlap.   The image forming apparatus according to claim 11, wherein the detection pattern is a combination of a part of latent image marks of each of the plurality of basic patterns overlapping each other. A storage means for storing a weighting factor of each latent image mark of the detection pattern;
15. The color misregistration correction unit performs color misregistration correction by weighting time information at which each latent image mark of the detection pattern is detected with a corresponding weight coefficient. The image forming apparatus described in the item.

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